(a) Field of the Invention
The present invention relates to an LCD (liquid crystal display) device and a method for manufacturing the same, and more particularly, to the structure of an LCD device having an orientation film suited to a rubbing treatment.
(b) Description of the Related Art
As is well known, an LCD device has a pair of substrates sandwiching therebetween an LC layer, wherein at least one of the substrates is transparent. By applying a voltage onto the LC layer to change the alignment state of the LC molecules, a desired image can be displayed on the LCD device while revealing the change of the alignment state by using a pair of polarizing plates.
An orientation film is generally used as a means for aligning the axes of LC molecules in a specified direction. The orientation film is obtained by a rubbing treatment wherein the orientation film is rubbed with a rubbing cloth such as rayon to form a plurality of minute stripe grooves on the surface of the orientation film. The LC molecules staying in contact with the orientation film are aligned in the direction of the stripe grooves. The alignment of the LC molecules can be changed by applying an external voltage onto the LC molecules thus aligned while adjusting the magnitude of the external voltage, thereby changing the amount of light passing through the polarizing plates.
It is to be noted that the rubbing treatment of the orientation film by using the rubbing cloth may involve a problem in that the orientation film is attached with a foreign particle and a scratch is formed on the surface of the orientation film due to the presence of the foreign particle during the rubbing. The foreign particle or the scratch on the surface of the orientation film disturbs the alignment state of the LC molecules, thereby incurring an undesirable luminance spot or an uneven luminance on the screen of the LCD device.
To avoid the above problem of the orientation film, the rubbing cloth is generally subjected to cleaning before the rubbing treatment. Although the cleaning may completely remove the foreign particles from the rubbing cloth, the above problem itself cannot be completely removed. More specifically, the rubbing cloth my be attached with a foreign particle staying in the area other than the display area before the rubbing treatment of the subject orientation film, or may be attached with a foreign particle during the prior rubbing treatment of another orientation film. In particular, the vicinity of the edge of the substrate on which the orientation film is formed may be contaminated by an etching residue generated during etching a multilayer film, or by a foreign particle generated by peeling-off of the multilayer film in the vicinity of the edge.
Patent Publication JP-A-2001-318380 describes a particle remover formed on a substrate of an LCD device. FIG. 5 shows the rubbing treatment in a perspective view, and FIG. 6 is a sectional view taken along line VI—VI in FIG. 5. As shown in FIG. 5, the particle removers 42 are disposed on both the front and rear edges of the substrate 40 on which an orientation film 41 is formed in the central area. The particle remover 42 extends in the direction normal to the direction in which the substrate advances during the rubbing treatment. As shown in FIG. 6, the particle remover 42 is formed by depositing an insulator film 42b on a stripe film 42a formed on the substrate 40, and includes a linear groove 42c formed on the insulator film 42b and a protrusion 42d disposed in the vicinity of the linear groove 42c on the insulator film 42b. 
The stripe film 42a is made of chrome which is generally deposited as a material for a black matrix for shielding the TFTs etc., whereas the insulator film 42b is made of silicon oxide which is deposited as an insulating film for the TFTs. The particle remover 42 has a length larger than the width of the orientation film 41.
In the rubbing treatment, as shown in FIG. 5, the substrate 40 is moved in the direction of arrow for rubbing by a rubbing cloth 11, which first contacts with the particle remover 42 before the rubbing treatment. The particle remover 42, as shown in FIG. 6, removes the particles 13 from the rubbing cloth 11 at the linear groove 42c and the protrusion 42d, whereby the rubbing cloth 11 is cleaned and then effects a rubbing treatment for the orientation film 41.
The conventional technique shown in FIGS. 5 and 6, however, complicates the fabrication process for the LCD device due to forming the particle removers 42 on the substrate 40 on which the orientation film 41 is formed. In addition, the particles removed by the particle remover 42 may contaminate the orientation film 41 by entering the area for the orientation film 41 during or after the rubbing treatment.
Patent Publication JP-A-9(1997)-43629 describes a dummy electrode area outside the display area, for removing particles generated by a rubbing treatment by a rubbing cloth. More specifically, as shown in FIG. 7, the LCD device includes a TFT substrate 40 and a counter substrate (not shown) sandwiching therebetween a LC layer and bonded together by using a sealing. The counter substrate includes a counter electrode along the alignment surface thereof.
The TFT substrate 40 has a transparent conductive film, and includes a central display area 46 and a peripheral dummy electrode area 47. As shown in FIG. 8, the central display area 46 includes therein an array of pixel electrodes 43 and associated TFTs acting as switching devices for the pixel electrodes 43. The peripheral dummy electrode area 47 includes therein a plurality of dummy electrodes 44 arranged in an array extending from the pixel electrodes 43 in the display area 46. A thin orientation film 41 made of polyimide, for example, is formed on the entire area of the TFT substrate 40 by using a printing technique.
The orientation film 41 is rubbed by a rubbing cloth 11 attached onto a roller 10. The foreign particles generated by the initial stage of the rubbing treatment by the rubbing cloth 11 are captured in the groove formed between the dummy electrodes 44 in the peripheral dummy electrode area 47, to thereby reduce the particles to be captured in the groove formed between the pixel electrodes 43 in the central display area 46. This reduces the possibility of a short-circuited failure caused by the particles captured between the pixel electrodes 43 in the display area 46.
The particles generated by the rubbing treatment are captured in the groove formed between the dummy electrodes 44, which are arranged at a specified pitch. The number of dummy electrodes for capturing the particles is limited, and accordingly, the amount of particles captured between the dummy electrodes 44 is not sufficient. In addition, the particles captured between the dummy electrodes may move to the central display area 46 to degrade the image quality of the LCD device.